Triacs are commonly used to regulate the proportional electrical power delivered to a load, and comprise the main power control element of a number of conventional dimmer switches used to control electrical lighting control loads. A triac gate signal controls the portion of the time during each normal alternating current half cycle during which the triac is conductive in order to vary the power delivered to a load and therefore to control the intensity of a load such as an electrical lighting fixture.
Although a triac can reduce the amount of power delivered to a load to the point at which the load is "effectively" off, a triac provides no means to open circuit a load or to completely disconnect a load from a source of electrical power. Therefore if the triac or some other component of a lighting control unit or system fails, it is conceivable that the device or system could fail in the closed condition in which power is delivered to the load. The triac or power control circuit used in normal operation could not then disconnect the load from the source.
For this reason, air gap switches that can open circuit the connection between a source and a load independently of a triac are required on dimmer switches. An air gap switch is required in dimmer switches used in the United States by Underwriters Laboratories (UL) Specification 172. A dimmer switch must meet the requirements of an appropriate specification of UL or some other recognized component testing agency in order to meet the requirements of the National Electric Code (NEC) and to meet applicable local electrical or building codes.
Air gap switches of various types are used in commercial dimmers or dimmer switches. One approach is to employ a conventional snap switch type toggle actuator as the main ON-OFF control and to provide a separate slider switch as an independent means for setting the intensity of the light or other load attached to the switch. U.S. Pat. No. 5,359,231 discloses a wall box dimmer of this type.
Other conventional dimmers use a rocker switch actuator that is pivoted about its centerline for local dimmer input. These switches do not use a conventional toggle type actuator, but employ a rectangular decorator type rocker that has either a flat or slightly inclined surfaces on the front of the rocker. These actuators engage two printed circuit board push button switches to provide UP-DOWN or BRIGHT-DIM inputs to power control circuitry located on the printed circuit board. Several different types of air gap switches are used with dimmers of this type. One approach is to use a general purpose printed circuit board slide switch that is located below one end of the rocker, typically the lower end. A slider actuator that includes a molded section engaging a slide switch actuator because this actuator is not exposed on the front surface of the dimmer. Touch dimmers also employ a general purpose slide switch with a specially molded slide actuator of this type.
Another type of air gap switch is disclosed in U.S. Pat. No. 4,783,581. That switch is formed of two contacts which are biased together in electrical contact by an elongated flat metal strip. A control lever is coupled to a cam. When the control lever is moved to the OFF position, the cam abuts the metal strip, forcing the strip to move in a direction opposite to its bias, thereby separating the two contacts and making electrical contact.
Still other air gap switches used in dimmer switches employ a metal leaf spring with a special contact button attached to its end. The spring holds the contact button in contact with a mating button, usually mounted on the printed circuit board to which the leaf spring is also attached. An actuator can moved into engagement with the leaf spring to force the air gap switch open. A commercial version of the dimmer switch shown in U.S. Pat. No. 5,283,516, manufactured and sold by Pass & Seymour Legrand is believed to use an air gap switch of this type. The air gap actuator used in that commercial product comprises a rotating ratcheting pin arrangement, believed to function in much the same manner as ball point pens to hold the air gap switch in an open position. A leaf spring switch is also shown in U.S. Pat. No. 4,988,840.
Another commercially available dimmer switch is manufactured by Lightolier Incorporated. The rocker used in that dimmer switch can be pivoted from a neutral position to a position in which a printed circuit board push button or key switch is activated. The OFF push button switch is actuated by a coil spring positioned between the rocker actuator and the push button or key switch. Further rotation of the rocker beyond the normal OFF position causes the actuator to open the air gap switch. The rocker engages a separate cylindrical post positioned in a tubular guide. This post opens a leaf spring contact, of the type described in U.S. Pat. No. 4,988,840, that has a contact button attached to the end to engage a contact mounted on the printed circuit board. The rocker of that prior art dimmer switch includes a detent or channel that is engaged by a ridge on a separate spring or clip to latch the rocker so that the air gap switch remains in the open position. This air gap actuator assembly includes a number of separate components that must be assembled. The additional assembly steps add to the manufacturing cost of the dimmer switch.